WIP: Implement APNG

third_party/WebKit/Source/platform/image-decoders/ImageFrame.cpp

 /*
  * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
  * Copyright (C) 2008, 2009 Google, Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 152 matching lines @@
 }
 
 void ImageFrame::zeroFillFrameRect(const IntRect& rect) {
   if (rect.isEmpty())
     return;
 
   m_bitmap.eraseArea(rect, SkColorSetARGB(0, 0, 0, 0));
   setHasAlpha(true);
 }
 
+static uint8_t blendChannel(uint8_t src,
+                            uint8_t srcA,
+                            uint8_t dst,
+                            uint8_t dstA,
+                            unsigned scale) {
+  unsigned blendUnscaled = src * srcA + dst * dstA;
+  DCHECK(blendUnscaled < (1ULL << 32) / scale);
+  return (blendUnscaled * scale) >> 24;
+}
+
+static uint32_t blendSrcOverDstNonPremultiplied(uint32_t src, uint32_t dst) {
+  uint8_t srcA = SkGetPackedA32(src);
+  if (srcA == 0)
+    return dst;
+
+  uint8_t dstA = SkGetPackedA32(dst);
+  uint8_t dstFactorA = (dstA * SkAlpha255To256(255 - srcA)) >> 8;
+  DCHECK(srcA + dstFactorA < (1U << 8));
+  uint8_t blendA = srcA + dstFactorA;
+  unsigned scale = (1UL << 24) / blendA;
+
+  uint8_t blendR = blendChannel(SkGetPackedR32(src), srcA, SkGetPackedR32(dst),
+                                dstFactorA, scale);
+  uint8_t blendG = blendChannel(SkGetPackedG32(src), srcA, SkGetPackedG32(dst),
+                                dstFactorA, scale);
+  uint8_t blendB = blendChannel(SkGetPackedB32(src), srcA, SkGetPackedB32(dst),
+                                dstFactorA, scale);
+
+  return SkPackARGB32NoCheck(blendA, blendR, blendG, blendB);
+}
+
+void ImageFrame::blendRGBARaw(PixelData* dest,
+                              unsigned r,
+                              unsigned g,
+                              unsigned b,
+                              unsigned a) {
+  *dest = blendSrcOverDstNonPremultiplied(SkPackARGB32NoCheck(a, r, g, b), *dest);
+}
+
+void ImageFrame::blendSrcOverDstRaw(PixelData* src, PixelData dst) {
+  *src = blendSrcOverDstNonPremultiplied(*src, dst);
+}
+
 SkAlphaType ImageFrame::computeAlphaType() const {
   // If the frame is not fully loaded, there will be transparent pixels,
   // so we can't tell skia we're opaque, even for image types that logically
   // always are (e.g. jpeg).
   if (!m_hasAlpha && m_status == FrameComplete)
     return kOpaque_SkAlphaType;
 
   return m_premultiplyAlpha ? kPremul_SkAlphaType : kUnpremul_SkAlphaType;
 }
 
 }  // namespace blink